1. Field of the Invention
The present invention relates in general to an automatic document feeder installed on a copying machine, and more particularly to an automatic document feeder which automatically separates and feeds one by one a plurality of documents set on a document feeding base by causing a document to be automatically separated, fed and recovered and permitting a next document to be automatically separated and fed, thereby successively copying the documents one by one, and to a method and apparatus for automatically controlling such a document feeder.
2. Description of the Prior Art
Some of known copying machines is preferably equipped with an automatic document feeder, i.e. what is called ADF, which, for the purpose of improving the document processing performance of a copying machine, permits a plurality of documents to be copied in a plurality of cycles by making the documents be automatically separated, fed and recovered cyclically.
Now, a representative example of the conventional ADF will be described in conjunction with FIGS. 1 to 3.
Referring to FIG. 1 which is a perspective view of the conventional ADF, the ADF generally comprises a document feeding base 1 , on which a plurality of documents 7 to be copied are consecutively set in the order of page numbers, and a recovered document base 2 on which recovered documents 9 after copying are piled up neatly.
FIG. 2 is a sectioned view taken along the section line A--A' of FIG. 1. As depicted in this drawing, the conventional ADF also comprises three driving parts, that is, a document feeding part including a document separating and feeding roller 3 and a pair of register rollers 4, a document conveying part including a conveyor drive roller 5 and a conveyor belt 6 supported between the drive roller 5 and a conveyor driven roller 5a and a document recovering part comprising a pair of ejection rollers 8.
Here, a circular encoder 10b is coaxially connected to a side of the conveyor drive roller 5 by means of a drive shaft 14 to which the encoder 10b and the drive roller 5 are commonly connected as depicted in FIG. 3 so that the encoder 10b rotates together with the conveyor drive roller 5. The encoder 10b is constructed to have a plurality of slits 13 which are radially and circumferentially formed as spaced apart from each other by predetermined intervals. On the other hand to cooperate with the encoder 10b there is provided an optical sensor 10c comprising a light emitting element 10d and a light receiving element 10e which are disposed at both sides of the encoder 10b to be aligned with the slits 13 of the encoder 10b. The light emitted from the light emitting element 10d is, therefore, intermittently received by the light receiving element 10e through the slits 13 as the encoder 10b rotates and this makes the optical sensor 10c output a pulse whenever the light is applied from the element 10d to the other element 10e through the slit 13.
In addition, the three driving parts, that is, the document feeding part, the document conveying part and the document recovering part, are provided with a drive motor (not shown), respectively, so that the known ADF necessitates at least three drive motors.
In the drawings, the reference numerals 10 denotes a document size sensing part and 10a is a register sensor of the document size sensing part 10.
In operation of the known ADF having the aforementioned structure, the documents 7, which are set on the document feeding base 1 with each of the documents turned upside down, are picked up one by one by the document separating and feeding roller 3 which then permits the picked-up document 7 to be fed to the document conveying part by way of the register rollers 4. Upon receiving the document 7 fed by the document feeding part, the document conveying part, which comprises the drive and driven rollers 5 and 5a and the conveyor belt 6, introduces the document 7 to a predetermined position on a contact glass (not shown) of the copying machine by conveying the document 7 which is laid thereon. At this position, the copying operation of the copying machine is carried out. After the copying operation, the copied document 7 is introduced between the ejection rollers 8 in order to be ejected from the driving parts of the ADF and piled on the recovered document base 2 with the document image face turned upwardly,
In the above process, it is required to accurately convey the document 7 so as to exactly align the front end of the document 7 with a reference copying position (shown at the arrow of FIG. 2) of the contact glass because the copying area of a copy paper (not shown) is determined according to the document position on the contact glass. This thus necessitates a document size sensing operation of the ADF, To achieve this sensing operation, the CPU of the ADF counts the number of pulses which has been applied from the optical sensor 10c thereto for a time interval between a time when the register sensor 10a of the document size sensing part 10 senses the front end of the document 7 and another time when the sensor 10a senses the rear end of the document 7, thereby detecting the document size, that is, the length of the fed document 7.
After the document size sensing operation, the conveyor belt 6 of the document conveying part conveys the document 7 to a reference copying position on the contact glass corresponding to the detected size of the document 7, thereby permitting the document to be exactly positioned on the copying position. The document 7 after the copying operation is then introduced between the ejection rollers 8 in order to be ejected from the driving parts of the ADF and piled on the recovered document base 2.
However in conveying the document 7 to the corresponding copying position on the contact glass in accordance with the length of the document 7 sensed by the document size sensing part 10, there may occur a slip of the document 7 relative to the conveyor belt 6 due to different sizes and weights of the documents 7 and this entails misalignment of the document 7 with the reference copying position on the contact glass. In result, the known ADF has a disadvantage in that it causes the document 7 to be prevented from being exactly copied. In addition as described above, the known ADF inevitably includes at least three drive motors because the three driving parts, that is, the document feeding part, the document conveying part and the document recovering part, are provided with a drive motor, respectively, and this entails increase of manufacturing cost. On the other hand, the known ADF generates a noise caused by solenoids and spring clutches which are inevitably provided to control the power transmission. Additionally, the motors, the solenoids and the spring clutches are obliged to make the known ADF be complex and this introduces a problem in maintenance of the ADF.
In an effort to solve the above disadvantages, there has been proposed other types of ADFs, for example, an ADF having a drive motor for commonly driving the document feeding part and the document conveying part or for commonly driving the document conveying part and the document recovering part. However, these types of ADFs have a disadvantage, respectively, in that they do not permit the parts, which are commonly driven by the drive motor, to be smoothly driven, Particularly, in the case of a known ADF additionally provided at the document feeding part thereof with a document pick-up assembly, an additional disadvantage is introduced due to a subsidiary control member, such as a solenoid for controlling the power transmission for the document pick-up assembly, or an additional drive motor for independently driving the document pick-up assembly.
On the other hand to solve the misalignment of the document with the reference copying position of the contact glass due to occurrence of the slip of the document relative to the conveyor belt, it has been proposed to provide a reversed directional movement function for the conveyor belt. However in this case, the conveyor belt has to start its reversed directional movement for a new document after the previous document has been completely discharged from the document recovering part and this arrangement also introduces a structural problem to the ADF because the ADF is inevitably provided with additional drive motor in consideration of the efficiency of copying work, that is, the copies per minute (CPM).